Enzyme cooperativity, theories and types SIMPLIFIED.

Enzyme cooperativity is an important phenomenon in the activity of enzymes and substrates.

It is important in explaining some phenomena such as the action of hemoglobin on oxygen carriage in blood.

Meaning

Enzyme cooperative is the phenomenon in which the shape of one active site subunits of an enzyme consisting of several active site is altered by a substrate or other molecules so as to change the shape/conformation of the second active. The second active site of the enzyme will differ in strength or velocity from that of the initial.

 

The enzymes or substrate of one pathway can cooperate with another pathway by providing a component that can act as a  regulator of that metabolic pathway.

In this ligand-enzyme interaction, it’s end means is to provide a conformational change in proximal and distal regions of the enzyme.

Theories of Enzyme cooperativity

There are many theories of Enzyme cooperativity. The outstanding ones are the ones to be discussed in this article. They are

  • MWC model
  • KNF model

MWC model

This theory is postulated from the work of three scientists namely Monod, Wyman and changeux. The theory is also known as symmetry model.

The model stated that “the subunits change shape in a concerted manner to preserve the symmetry of the entire molecule as it was transformed from one confirmation t20 2nd confirmation are under the influence of a ligand

KNF model

This theory was also proposed by three scientists. The three scientist Koshland, Nemethy and Filmer. This theory of cooperativity is also known as induced or sequential model. The theory states that ” each subunit changed shape as ligand bound, so that changes in one subunit lead to distortions in the shape  or interaction of other subunits of the protein“.

This theory of enzyme cooperative explain both positive cooperativity and negative cooperativity.

 

Types of enzyme cooperativity

There are two types of cooperativity which are,

Positive cooperativity : in this type of cooperativity, a change in the confirmation of the subunit, lead to an increased or easy binding of the subsequently ligand or substrate. Hence, more of the substrate of the second, third, etc will bind to the active site. It is termed positive cooperativity due to the increase in the activity of the enzyme or protein.

Negative cooperativity : in this type of cooperativity, the change in conformation made the binding of the subsequent ligands or substrate difficult. There is reduced activity of the subsequent subunits of the enzyme. This lead to the term negative enzyme cooperativity.

Enzyme cooperativity
Graph of cooperativity

We can use haemoglobin to explain positive and negative enzyme cooperativity.

Hemoglobin is a protein with a haem and a globin strand. it is found in red blood cells and helps in the transport of oxygen throughout the animal it is found.

When an oxygen atom binds to one of hemoglobins four binding sites, the affinity to oxygen of the three remaining, the affinity to oxygen of the three remaining binding site increases. Hence, it  depicts a positive enzyme cooperativity. Oxygen is more likely to bind to haemoglobin.  There is higher affinity of oxygen when compared to the unbound haemoglobin (negative enzyme cooperativity).

Without cooperativity, haemoglobin will not efficiently transport oxygen in the lungs, with the help of lung surfactants.

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